Hitherto, polyether compounds such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol, etc., have been widely used as raw materials for resins, such as polyurethanes, for coatings, adhesives, molding materials, etc.
Many of these polyether compounds have hydroxyl groups at the terminal portion thereof, which causes a problem in that the scope of applications for use is restricted in the case of using them as a raw material for resins.
For the purpose of overcoming this problem, polyether compounds having an allyl group at the terminal portion thereof, which are prepared by polymerizing the glycidyl ether, and polyester compounds having a vinyl group at the terminal portion thereof, which are prepared by thermal decomposition of polypropylene glycol, etc., have been used.
However, many resins obtained by using these compounds are insufficient in hardness and strength, even though they have excellent flexibility because the molecular structure of these compounds is straight chain.
On the other hand, epoxy resins which have been widely used in industry include so-called epi-bis type epoxy resins produced by reacting bisphenol A and epichlorohydrine.
These resins have advantages, e.g., various products can be obtained, from a state of liquid to solid, and they can be cured at room temperature with polyamines because reactivity of epoxy resins is high.
However, cured products thereof have faults in that the weatherability is inferior, electric properties such as anti-tracking property, etc., are inferior, and the heat distortion temperature is low, although they do have desirable characteristics of good water resistivity and strength.
In recent years, particularly epoxy resins prepared by reacting phenol resin or novolak resin with epichlorohydrin have been used as resins for encapsulating VLSI (very large scale integrated circuit), etc., but chlorine contained in the resins, typically in an amount of several hundred parts per million, causes the problem of deteriorating the electric properties of such electronic devices.
Epoxy resins having excellent electric properties and heat resistance which do not contain chlorine are known, such as certain alicyclic epoxy resins.
These have been produced by an epoxidation reaction of a compound having a 5- or 6-membered cycloalkenyl structure.
The epoxy group in these resins is the so-called inner epoxy group, and curing is usually carried out with acid anhydrides by heating.
However, since reactivity is low, they cannot be cured with polyamines at room temperature.
Therefore, use of the alicyclic epoxy resins is restricted within a very narrow scope.
As alicyclic epoxy resins, those having a structure represented by formula (I) or (II) have been industrially produced and used. ##STR1##
(I) has been used as a heat resistible epoxy diluent, because of having a very low viscosity, but it is high in toxicity and causes the problem of poisoning upon contacting skin of the human body.
(II) contains only small amounts of impurities and has low color hue, and cured products produced therewith have a high heat distortion temperature, but its use involves problems of inferior water resistivity due to the ester bond.
In addition, because (I) and (II) are liquid state epoxy resins having a low viscosity, it is impossible to apply molding systems for solid epoxy resins, such as transfer molding, etc., to them.
From the above viewpoint, novel alicyclic epoxy resins which have oxycyclohexane units had been disclosed in Japanese Application Laid-open No. 166675/1985 (=U.S. Pat. No. 4,565,859).
However, the epoxy resins disclosed in Japanese Application Laid-open No. 166675/1985 were only obtained as those having relatively low softening temperatures.
Therefore, the epoxy resin produced by the above described process has been used by adding thereto a blocking inhibitor such as calcium stearate, etc., because they apt to bring about blocking (i.e., adherence of layers to each other) especially when left at high temperatures in summer.
However, the addition of a blocking inhibitor deprives them of general-purpose properties.
Furthermore, there is not only the matter of overcoming the above described problems, but as the number of methods or objects involving use of epoxy resins have grown, so have the desired characteristics of such epoxy resins; for example, epoxy resins having higher softening temperature, excellent water resistance, and excellent ductility, have increased.
From the above viewpoint, improvements in epoxy resins such as that disclosed in Japanese Application Laid-open No. 166675/1985 have been required.